Method and apparatus for joining aircraft components

ABSTRACT

The surface of a moulding tool, for receiving a first aircraft component, for example a spar, is shaped to correspond to the surface of a second aircraft component, for example a wing skin. A gap is defined between the tool and the first component. Resin is drawn into the gap by a suction pump. The resin fills the gap and cures to forma shim. The first and second components, which are in the form of composite material structures, are then joined together without any significant voids being formed therebetween.

The present invention relates to a method of joining two aircraftcomponents and in particular to a method of enabling two aircraftcomponents to be joined together, wherein the surfaces of the aircraftcomponents to be joined together are so shaped that a gap is definedtherebetween and the method includes producing a shim so that the gapmay be substantially filled.

When manufacturing aircraft structures, such as for example wings, it isnecessary to join one aircraft component to another. It is often thecase that aircraft components are manufactured in such a way that whenjoining two components a shim is needed to fill a gap between thecomponents. The use of a shim when joining components together iscommon, for example, when joining composite material aircraft structuressuch as spars and wing skins, owing to difficulties in manufacturinglarge composite parts accurately to a pre-defined shape. Generally,after a composite component has been moulded to a particular shape, thecomponent changes shape due to effects such as the shrinkage of theresin matrix and other material effects in view of the temperatures ofdifferent regions of the material in the mould and in view of thedifferent fibre lay-up directions employed. Such a change in shape isgenerally referred to as “spring back”. Predicting accurately how much acomponent will spring back after moulding is difficult, if notimpossible. It is therefore difficult for component manufacturers toassemble composite components to the tight tolerances required forefficient aircraft production and operation. It may therefore beaccepted that such components will spring back, and that the componentsto be joined together will not, without employing further means, fittogether exactly (or close enough to be within acceptable tolerances).Thus, such components may be manufactured such that there will be a gap,albeit small, between adjacent components that is filled during assemblyby means of a shim.

Shims have, to date, been produced by various techniques includingmachining a solid shim from a separate piece of metal material (such asa piece of aluminium). Solid shims are machined and fettled to fit inthe gap and then sealant is used to fix the shim in the gap. Suchmachining/fettling is time consuming and requires a skilled operator.

Shims have also been produced with the use of sealant without employingany metal pieces. Forming a shim with sealant may be effected by coatingeither or both surfaces to be joined with sealant, then bringing thesurfaces together so that the sealant is squeezed between the componentsand out from between the components, thereby filling the gap withsealant. Excess sealant squeezed out of the gap is then wiped away.Joining one component to the other using sealant in this way can lead tovoids being present between the two components, where insufficientsealant has been provided. Also, filling gaps with sealant in such a waycan be inefficient and can even reduce the effectiveness of the joinbetween the two components.

It is an object of the present invention to provide a method and anapparatus which enables two aircraft components to be joined togetherwhich avoids or mitigates one or more disadvantages associated with theabove described prior art.

According to the present invention there is provided a method ofenabling two aircraft components to be joined together, the methodincluding the steps of providing a first aircraft component having asurface to be joined to a corresponding surface of a second aircraftcomponent, the first and second components being so shaped that ifjoined there would be a gap defined between said surfaces of the firstand second components, providing a resin infusion system comprising asource of resin, effecting flow of the resin from the source of resininto the gap by means of suction, thereby substantially filling the gapwith resin, and curing the resin. A shim may thereby be formed.

Thus, during performance of the method of the present invention resin iscaused to flow into and to fill substantially the entire gap, therebyreducing the chance of there being a void in the shim so formed thatmight affect the structural integrity of the join, once the secondaircraft component is joined to the first aircraft component. The methodmay also be of particular advantage in that when the components areassembled no shimming need take place on the production line.

The method is preferably so performed that the resin is cured on thefirst aircraft component.

The method is of particular advantage when the gap has at least oneregion having a thickness of greater than 0.2 mm. The gap may have athickness, over at least 95% of the area of the gap, of less than 3 mm.Preferably, the gap has a maximum thickness of less than 3 mm. The gapmay have a varying thickness, such that the thickness might vary withina range of between 0 mm and 3 mm. For example, the gap may have bothregions having a thickness of less than 0.7 mm and regions having athickness of greater than 0.7 mm. The gap may be so shaped that it hasat least one region having a thickness of less than 0.5 mm and at leastone region having a thickness of greater than 1.0 mm.

The flow of the resin out of the gap is advantageously restricted bymeans of a barrier. The barrier may for example be placed such that asurface of the barrier is positioned along at least a part of theboundary of the gap. The barrier may be in the form of a part of thesecond aircraft component. Alternatively, the barrier may be distinctfrom the second aircraft component.

At least a part of the barrier is advantageously formed by a surface ofthe resin infusion system. The surface of the resin infusion system thatforms the barrier (or part thereof) may for example be in the form of apart of a moulding tool that forms a part of the resin infusion system.The surface of the barrier that faces the surface of the first componentis preferably shaped to correspond to said surface of the secondaircraft component.

The barrier is, during the filling of the gap with resin, preferablyremovably, for example temporarily, fixed in position relative to thefirst aircraft component. Even in the case where the barrier is formedby the second component, the first and second components are preferablyremovably fixed, so that, for example, after the shim is formed thefirst and second components may be separated to allow subsequentassembly of the components to each other and in relation to othercomponents. A surface of the first or second aircraft component may beprepared so that the adherence of the resin to the surface is improved.A surface of the first or second component may be prepared so that theadherence of the resin to the surface is reduced, to facilitate laterseparation of the surface from the cured resin. The surface may beroughened by, for example, grit blasting, to improve its bondingproperties. The surface may be smoothed, for example by applying acoating such as, for example, a release agent, to reduce its bondingproperties. Whilst it is preferred that the resin once cured bonds tothe first component, and the first component together with the curedresin, on the one hand, and the second component, on the other hand, areonly fixed together during final assembly, it is within the scope of thepresent invention both for the cured resin to be releasable from boththe first and second components and for the resin to be bonded to boththe first and second components immediately after curing of the resin.

The process may thus also be used to bond surfaces together; in thatcase, each surface may be prepared so that the adherence of the resin tothe surface is improved; thus a surface of the first aircraft componentand a surface of the second aircraft component may be so prepared.

In the case where the barrier is a surface defined by the resin infusionsystem, the first aircraft component may be removably, for exampletemporarily, fixed in position relative to the resin infusion system.The resin infusion system may include a locating element that engageswith a corresponding element on the first aircraft component. Thebarrier may include a locating element that engages with a correspondingelement on the first aircraft component. Such a locating element mayassist in fixing the first aircraft component in the desired positionrelative to the barrier. The method may include a step of machining, orotherwise forming, a hole in the first aircraft component, the holebeing configured to receive the locating element. There may be more thanone locating element. Preferably there are at least two locatingelements. The second aircraft component may include one or more holes.Such holes may aid alignment of the first and second aircraftcomponents. The first and/or second aircraft components may also includeone or more locating elements. One or more locating elements mayalternatively or additionally be provided separately.

The barrier is preferably fixed to the first aircraft component by meansof a pressure difference. A vacuum pump may for example be used to causethe pressure difference. A vacuum pump may be used to provide thesuction that draws the resin into the gap. Advantageously, a singlevacuum pump is used both to cause the pressure difference that fixes thebarrier to the first aircraft component and to provide the suction thatdraws the resin into the gap. The single vacuum pump may however beviewed as being the only common part of two distinct suction systems.

A filter is preferably provided to hinder, or preferably substantiallyrestrict, flow of the resin out of the gap. The filter is for exampleplaced at the boundary of the gap and the source of suction and allowsair to be drawn from the gap, whereas the flow of resin through thefilter is hindered. Preferably the filter is so configured that duringperformance of the method less than 1% of the resin introduced into thegap escapes out of the gap via the filter.

The resin infusion system preferably includes a plurality of resinports, through which resin passes and then into the gap. The pluralityof resin ports may for example be in the form of outlets, holes,passages, channels or the like. The plurality of resin ports may beprovided along the length of a conduit. For example, in the embodimentof the invention described below with reference to the drawings, acoiled spring is provided that in use is sealed along its length arounda section of its circumference so that it acts as a pipe with a seriesof ports, in the form of apertures, along its length. A toothed belt mayalternatively or additionally form part of the structure defining theresin ports.

Preferably, the resin infusion system includes a plurality of suctionports to which the suction is applied. The plurality of suction portsmay for example be in the form of holes, passages, channels, suctioninlets or the like. The suction ports may be formed in the firstaircraft component. The suction ports may alternatively or additionallybe formed in a barrier (for example the barrier mentioned above) oranother component, such as the second aircraft component, for example.

The first aircraft component may include at least one aperture arrangedso that the suction is provided via said at least one aperture. Forexample, in the embodiment of the invention described below withreference to the drawings, the first aircraft component is in the formof a wing spar and ports are provided as holes in the spar that passfrom one surface of the spar to an opposite surface of the spar. Suchholes may for example perform at least one other purpose. For example,in the embodiment described below the holes are in the form of pilotholes that are present in the spar for the purpose of fixing ribs to thespar. Advantageously, substantially all apertures or holes in the firstcomponent that are used in the method perform another purpose orfunction. The method may therefore be performed without needing tomachine any holes other than those that would in any case have beenmachined.

The curing of the resin is conveniently effected by a cold curingtechnique. Whilst possible, the resin is preferably not heated prior tobeing drawn into the gap. The resin may be allowed to cure at atemperature below 40 degrees Centigrade, preferably at a temperaturebetween 0 and 30 degrees Centigrade. Preferably the resin is cured at,or close to, room temperature.

The method is preferably so performed that the difference in pressurebetween the source of suction and the source of resin is less than 2bar. Preferably the pressure difference is less than 1.5 bar. Morepreferably the pressure difference is 1 bar or less. The pressuredifference is preferably at least 0.1 bar. The resin may be supplied ata pressure substantially equal to atmospheric pressure. It may beadvantageous, for example depending on the choice of resin, for theresin to be supplied at a pressure above atmospheric pressure. Theafore-mentioned pressure differences are preferably maintained for atleast the majority of the duration of the step of filling the gap withresin and more preferably for at least 90% of the duration of that step.

The method may include a step of reducing the suction applied, butmaintaining a pressure gradient. Such a step is preferably performedafter the resin has substantially filled the gap. Thus the firstcomponent, if deformed by means of the pressure difference appliedduring the filling of the gap with resin, may relax and conformsubstantially to its original shape.

The method may include a step of placing solid material in the gapbefore effecting flow of the resin into the gap. For example, if the gaphas regions of a certain thickness of greater than, say, 0.7 mm, it maybe beneficial for the resin in such regions to be strengthened by meansof solid material. The solid material preferably comprises fibres. Thesolid material may for example be in the form of a dry woven cloth, forexample a carbon fibre cloth or a glass fibre cloth. The methodpreferably includes a step of assessing which regions of the gap have athickness greater than a predetermined threshold thickness. Solidmaterial may thereafter be placed in the regions so identified. Thepredetermined threshold thickness is preferably within the range of 0.6mm to 1 mm.

The resin is preferably a relatively low viscosity resin. Preferably,the resin has a viscosity of less than 1000 centipoises and morepreferably of less than 800 centipoises. The resin may for example havea viscosity in the range of 400 to 750 centipoises.

Higher viscosity resins may be used, in alterative embodiments of theinvention; the necessary pressure gradient may be provided by applying asufficiently high pressure at a resin inlet and a relatively lowpressure (preferably a vacuum) at a resin outlet.

The method has particular application when at least one of the aircraftcomponents to be joined are formed of a composite material. Thus thefirst and/or the second aircraft components may be formed of a compositematerial.

The method may further include a step of joining the second aircraftcomponent to the first aircraft component, for example during finalassembly of the components. In an embodiment of the invention describedbelow with reference to the drawings, the first aircraft component, inthe form of a wing spar, is mounted on a moulding tool during the stepof filling the gap with resin. In such a case, the first aircraftcomponent would of course be removed from the moulding tool togetherwith the cured resin before joining the first and second aircraftcomponents. In another embodiment the first and second components areplaced together as if being joined, a shim is formed therebetween, thefirst component and shim are then separated from the second component,and then the components are finally assembled. Sealant may be used whenbonding the first component and shim to the second component.

Preferably, one of the first and second components is a spar, or partthereof. Preferably, one of the first and second components is a wingskin, or part thereof. For example, the first aircraft component may bea wing spar and the second aircraft component may be a portion of wingskin. In an embodiment described below the first aircraft component is acover (a portion of the wing skin) and the second aircraft component isa spar, the surfaces to be joined being defined by a flange of the sparand a portion of the cover.

The aircraft components to be joined and the way in which the method isperformed may be such that the resin once cured can be considered asbeing in the form of a shim. In such cases, the method may be viewed asbeing a method of forming a shim.

The invention also provides a method of preparing a first aircraftcomponent before final assembly of the first aircraft component with asecond aircraft component, the method including the step of forming ashim by a vacuum resin infusion technique, the shim so formed enablingthe gap that would otherwise be defined between the first and secondaircraft components when finally assembled to be reduced. The inventionalso provides a method or preparing an aircraft component before joiningthe component to another component, the method including the steps ofproviding a first aircraft component and a shim tool having a surfaceshaped to correspond to the surface of a second aircraft component towhich the first component is to be joined, arranging the surface of theshim tool and the first aircraft component against each other, therebyforming a gap between the tool and the component, and causing the shimtool to fill the gap with a shim produced by a vacuum resin infusiontechnique. Features described above in relation to the invention may ofcourse be incorporated into these aspects of the invention. Theinvention also provides shim forming apparatus including a jig forreceiving and positioning a first aircraft component relative to asecond aircraft component, the apparatus further including a resininfusion system including a suction pump and a source of resin, theapparatus being so arranged that in use a gap defined between thesurface of the second aircraft component and the first aircraftcomponent may be filled with resin to form a shim.

The invention yet further provides a shim forming apparatus including amoulding tool having a surface shaped to receive a first aircraftcomponent such that a gap is present between the surface of the mouldingtool and the first aircraft component, the surface of the moulding toolbeing shaped to correspond to the surface of a second aircraftcomponent, the apparatus further including a resin infusion systemincluding a suction pump and a source of resin, the apparatus being soarranged that in use the gap between the surface of the moulding tooland the first aircraft component may be filled with resin to form ashim.

The moulding tool may have a portion that in use is able to sealinglyengage with a portion of the first aircraft component, to define asealed region, which is connectable to a suction pump so that in usesuction may be applied to the region, thereby holding the first aircraftcomponent in a fixed position relative to the moulding tool. Theapparatus may further include a vacuum bag that is attachable to themoulding tool and which, in use, enables suction to be applied to themoulding tool to draw resin from the resin source into the gap.

The invention also provides a moulding tool suitable for use in a shimforming apparatus, the moulding tool having a surface shaped to receivea first aircraft component such that a gap is present between thesurface of the moulding tool and the first aircraft component, thesurface of the moulding tool being shaped to correspond to the surfaceof a second aircraft component, the moulding tool being so configuredthat it may be arranged so that a gap formed between the surface of themoulding tool and such a first aircraft component may be filled withresin to form a shim.

The invention further provides an aircraft component and shim asproduced by the method or apparatus of the invention. There is alsoprovided an aircraft structure including a first aircraft componentconnected to a second aircraft component, there being a shim interposedbetween the first and second components the shim being produced by themethod or apparatus of the invention. There is yet further provided anaircraft including such an aircraft structure.

Of course, it will be appreciated that features described in relation toone aspect of the present invention may be incorporated into otherdifferent aspects of the invention. For example, the method of theinvention may be performed with the shim forming apparatus or mouldingtool of the invention. Also, the shim forming apparatus or moulding toolof the invention may be arranged or configured to be suitable for use inthe method of the invention.

By way of example embodiments of the invention will now be describedwith reference to the accompanying schematic drawings, of which:

FIG. 1 is a plan view of an aircraft,

FIG. 2 a is a cross sectional view of a wing of the aircraft shown inFIG. 1,

FIG. 2 b shows a magnified view of a part of FIG. 2 a,

FIG. 3 is a partial cross sectional view showing a spar, a toolaccording to a first embodiment and a shim formed therebetween,

FIG. 4 shows a partial perspective view of the tool shown in FIG. 3without a spar,

FIG. 5 shows a perspective view of the tool shown in FIG. 3 with a sparon the tool,

FIG. 6 shows a cross section of the tool and spar,

FIG. 7 shows a cross section of the tool and spar during operation ofthe tool,

FIG. 8 is a cross-section of a spar flange and cover between which ashim is being formed in accordance with a second embodiment,

FIG. 9 is a cross-section of the cover shown in FIG. 8 after the shimhas been formed,

FIG. 10 shows a cross-section of the tool and spar, according to a thirdembodiment of the invention,

FIG. 11 shows a cross-section of the tool and spar of FIG. 10 duringoperation of the tool,

FIG. 12 is a section through the line A-A in FIG. 11,

FIG. 13 is a cross-section of a spar flange and cover between which ashim is being formed in accordance with a fourth embodiment, and

FIG. 14 is a cross-section of a spar flange and cover between which ashim is being formed in accordance with a fifth embodiment.

FIG. 2 a shows a cross section taken along the line A-A of the wing 1 ofthe aircraft 2 shown in FIG. 1. The wing 1 comprises a front wing spar 3a and a rear wing spar 3 b that run along the leading and trailing edgesof the wing 1. The spars 3 are generally C-shaped in cross section. Ribs4 are attached to and between the spars 3 a, 3 b. Attached to the spars3 a, 3 b and the ribs 4 are the upper wing skin 5 a and lower wing skin5 b.

The spars 3 a, 3 b and wing skins 5 a, 5 b are each formed fromcomposite carbon fibre and matrix materials.

FIG. 2 b shows a magnified view of a portion of FIG. 2 a in the regionof the interface between the front wing spar 3 a and the lower wing skin5 b. Owing to the manufacture and assembly process and in particular dueto the change in shape of the spar after demoulding (known as“springback”), a gap is present between the spar 3 a and the wing skin 5b. This gap is filled by a shim 6. The shim 6 is formed in the gapbetween the spar 3 and the tool 9 by means of a resin vacuum infusionprocess.

FIG. 3 shows a cross section of a part of a tool 9 for making such ashim 6.

With reference to FIG. 3, the C-shaped cross section of the spar isdefined by two flanges 8, between which there extends the spar web 7,the flanges 8 each extending from the web 7 in a direction that isapproximately transverse to the web 7.

In this first embodiment illustrated by FIGS. 1 to 7, the rear spar 3 bis 11.5 metres long and at the root end has a web depth of 250 mm, aflange height of 150 mm and a laminate thickness of 15 mm. Thecorresponding dimensions at the tip end of the spare, are a depth of 150mm, a flange height of 45 mm and a laminate thickness of 6 mm.

The shim 6 extends along the majority of the length of the spar and hasa width that varies between 0 and about 1.5 mm, a height that variesbetween about 40 mm and about 150 mm and a length of about 11.5 m.

The outer surface of the tool 9 that opposes the surface of the flange 8of the spar 3 is shaped to correspond to the surface of the wing skin 5to which the spar 3 is to be attached.

FIG. 4 shows the main parts of the tool 9 in perspective. The tool 9,made from polyurethane material, is mounted on a steel support base 10.In the first embodiment the tool is made from CIBATOOL (RTM) BM5460polyurethane block available from Vantico Limited (UK), although othersuitable materials such as epoxy materials could be used. The tool 9 isof a shape suitable to receive a spar 3 (not shown in FIG. 4). Thus thetool 9 has a base 11 and side portions 12 extending upwardly from thebase such that the web 7 of the spar sits on the base 11. The flanges 8of the spar extend upwardly and in the same general direction as theinner surfaces of the side portions 12, a small gap being definedbetween them and the spar, in which gap the shim 6 is to be formed. Thebase 11 has a rebate 13 formed therein in which foam sealant tape isaccommodated. The tool 9 also includes two locating pins 14, oneprovided at each end on the base 11 of the tool 9.

FIG. 5 shows a spar 3 positioned on the tool 9. The spar 3 has two holesin which the locating pins 14 are accommodated, so that the spar 3 iscorrectly positioned on the tool 9. The spar 3 has further holes (notshown in FIG. 5) in the web 7 of the spar 3 that provide fluidcommunication between the underneath of the spar in the region definedby the sealant tape in the rebate 13 and the uppermost side of the spar3. Bag tape 15 (such as GS-100 bag tape, available from AirtechInternational, Inc) is provided around and encompasses those holes. Thespar 3 has further pilot holes 16 machined along its length in eachflange 8 of the spar 3, only two pilot holes being shown in FIG. 5. Whena wing is assembled, ribs are attached to the spar 3 via the pilot holes16 by means of rivets, bolts or the like.

FIG. 6 shows a cross section of the spar 3 and tool 9 shown in FIG. 5and additionally shows various other features/components omitted (forthe sake of clarity) from FIG. 5. FIG. 6 shows the holes 18 provided inthe web 7 of the spar 3 that are encompassed by the bag tape 15. Overthe holes 18 there is placed a breather mat 17 (such as an Airweave N-10breather from Airtech International Inc). FIG. 6 additionally showsbrakes 19 placed along the length of the spar and over the pilot holes16, the brakes 19 being in the form of a strip of carbon fibre (dryfibre). Resin inlets, in the form of coil springs 20 which act as pipes,are provided on the top of each of the flanges 8 of the spar 3. Thecoils of the springs are spaced apart so that in use resin may flow outof the spring through the gaps between adjacent coils. (The resin inletscould of course equally be referred to as resin outlets, since resin isin use caused to flow out of the coils of the spring.) Bag tape 21passes along the length of the top of the interior surface of the sideportion 12 of the tool 9. Bag tape 22 also passes along the top of theinterior surface of the flange 8 of the spar 3.

A shim 6 is formed in the gap between the side portions 12 of the tooland the flanges 8 of the spar 3 by means of a process that will now bedescribed with reference to FIGS. 5, 6 and 7 of the drawings.

FIG. 7 shows schematically the function of a vacuum bag 30 and thedirection of the flow of fluids in the system. As a first step, surfacesof the spar 3 are suitably prepared and the various holes are machinedin the spar, for example, by drilling. The spar is then placed on thetool such that the locating pins 14 are received in the appropriateholes in the web 7 of the spar 3. The bag tape 15 is then applied aroundthe holes 18 in the web of the spar 3. A breather mat 17 is then placedover the holes 18. The vacuum bag 30, attached to a vacuum pump (notshown), is attached to the bag tape 15, the relevant sealed section ofthe bag being represented in FIG. 7 by the reference numeral 23. Thepump is operated to draw air from the bag and spar arrangement therebydrawing the web 7 of the spar 3 on to the tool 9 by virtue of thenegative pressure caused between the spar 3 and the tool 9 in the regionsealed by the seal in the rebate 13. The breather mat 17 prevents thevacuum bag from sealing over the holes 18, which would prevent air frombeing drawn from the sealed region beneath the spar web 7.

A pressure drop test is then performed to test the integrity of the sealbetween the spar and tool. If the vacuum pressure drop test issuccessful then brakes 19 are installed over holes 16 and the bag 30 isattached to the bag tapes 21 and 22 on the flange 8 and the spar 3,respectively, these sections of the bag being represented in FIG. 7 bythe reference numerals 24 and 25.

The purpose of the section 25 of bag 30 over the resin inlets 20 is toprevent resin from “fast tracking” from the inlet 20 via an undesiredroute to the vacuum pump. The bag 30 is thus temporarily sealed on allsides to the tool 9 by means of the bag tape.

After the bag 30 has been attached to the flanges 8 of the spar 3, toform sections 24, 25, a further vacuum pressure drop test is performed.If that pressure drop test is successful, then the resin inlets areopened so that resin including a hardening agent may flow from a resinsource (not shown), via the inlet pipes 20, into the gap between theside portions 12 of the tool 9 and the flanges 7 of the spar 3.

Suction is then applied to the bag 30 such that the bag 30 is drawn flatagainst the surface of the spar 3. For example, sections 25 of the bag30 seal over spring 20, which has the effect both of converting spring30 into an arrangement similar to a pipe with an open side and ofpreventing resin from flowing over the spar 3 as opposed to flowing intothe gap between the spar 3 and the tool 9.

Resin is drawn from the inlets 20 into the gap between the flanges 8 ofthe spar 3 and the tool 9 and towards the outlet holes 16. The resinenters the inlet 20 at one end of the spar 3 and the suction provided bythe vacuum pump is applied at the other end of the spar 3 in the regionof the boundary between the flange 8 and web 7 of the spar. The resin isconsequently drawn from one end of the spar to the diagonally oppositeend. The flow of the resin is such that the resin generally flows downfrom the inlet pipe 20 to the nearest pilot hole 16 opposite and belowthe resin in the pipe 20. The resin progresses gradually along thelength of the spar filling successive pilot holes 16, thereby graduallyfilling the gap. Resin is prevented from exiting the outlet holes 16 bymeans of the brakes 19. The vacuum pump that causes the resin to bedrawn into the gap between the spar 3 and the tool 9 is operated untilresin is witnessed in the brake 19 above each of the outlet holes 16.After the gap has been completely filled with resin, the vacuum pump isoperated to increase the pressure from close to zero bar to about 0.2bar, which allows the spar flanges 8 to relax gradually. The vacuum pumpis, after a suitable length of time, switched off completely. The resinis then allowed to cure at room temperature for 24 hours. The curedresin thus forms a shim.

The resin used in the above described embodiment is a low viscosityresin that cures at room temperature and is able to flow freely under arelatively low pressure gradient (pressure differences of 1 bar at thevery maximum) such as LY5052/HY5052 (an epoxy resin and hardeneravailable from Vantico Limited).

After the resin has cured, the vacuum bag 30 is removed and the spar 3and shim 6 are removed from the tool 9. The spar 3 and shim 6 may thenbe used in standard assembly techniques to form part of a wing skin, awing skin being attached to the flange 8 of the spar 3 via the shim 6with standard joining techniques.

FIG. 8 shows schematically a cross section of a spar 3 and a cover whichforms part of the wing skin 5 b according to a second embodiment of theinvention. The spar flange 8 is positioned on the wing skin 5 b in orderto enable a shim 6 (not shown in FIG. 8) to be formed in the gap or shimcavity 40 between the two aircraft components. Resin inlets in the formof a coil spring 20 which acts as a pipe are provided along the edge ofthe spar flange 8 in a manner similar to that described above inrelation to the first embodiment. In this embodiment, however, a toothedbelt 41 is additionally provided to improve the flow of resin. The belt41 separates the inlet spring 20 and the spar flange 8 to providechannels that allow resin to pass into the shim cavity 40. A singlestrip of vacuum film 43 is used to seal the joins between the wing skin5 b, the inlet spring 20 and the spar flange 8. The vacuum film 43 issealed at the edges to the spar 3 and the wing skin 5 b by strips oftacky tape (bag tape) 21, 22. A packer 42 is provided on top of thetoothed belt 41 to prevent a cavity being formed due to bridging of thevacuum film 43 between the spar flange 8 and the inlet spring 20. Apilot hole 16 in the wing shim 5 b is covered on the opposite side tothe spar flange 8 by a brake 19 in the form of a bleed pack. A source ofvacuum (not shown) is connected directly to the brake 19, the suctioncausing flow of air (initially) in the direction of the arrow B. The gapbetween the spar flange 8 and the wing skin 5 b is sealed at the edge,remote from the spring 20, by means of bag tape 44 and an ‘O’-ring seal45 which prevents the tape 44 from being drawn into the shim cavity 40by the vacuum.

Prior to arranging the components in the manner as shown in FIG. 8, thespar flange 8 is treated with release agent (in this case a wax) toprevent the resin from adhering to the spar 3 and the wing skin 5 b istreated by grit blasting to prepare a surface which will adhere well tothe resin, once cured.

In use, sealant flows from the spring 20 in the direction of the arrowsA through the toothed belt 41 into the shim cavity 40 drawn by thevacuum from the direction of arrow B. Once the shim cavity is filled,any excess resin is drawn through the pilot hole 16 and to the brake 19.The resin is then left to cure to a shim 6. The spar 3 is then removedalong with the consumables (i.e. the tacky tape 21, 22 and 44, thepacker 42, the ‘O’-ring 45 and the spring inlet 20) to leave behind thecured shim 6 adhered to the wing skin 5 b as shown in FIG. 9.

The pilot hole 16 is then redrilled to remove any cured resin.Alternatively, the pilot hole 16 in the wing skin 5 b may be backdrilled prior to removal of the spar 3 to provide a hole through boththe spar flange 8 and the wing skin 5 b to accept fasteners to enablethe wing skin 5 b and the spar 3 to be fastened together.

In a further alternative arrangement (FIGS. 10 to 12), the brake 19 ofthe first embodiment is replaced by a brake (filter) arrangement 119comprising a brake 105 that is separated from the surface of the spar 3by a length of tubing 110. According to this third embodiment, tube 110is attached by a connector 115 to pilot hole 16. Brake 105 is connectedvia further tubing 120 to a vacuum pump (not shown).

Brake 105 (FIG. 12) comprises a length of flat tubing 130, of a similarlength to its width, containing a brake medium 140 sealed at each end bybag tape 135, through which tubes 110 and 120 pass.

In use (FIG. 11) vacuum bags 123, 125 are attached in placescorresponding to bag sections 23, 25 in FIG. 7. Air flows through brake119 initially in the direction of arrow C. Once the shim cavity isfitted, any excess resin is drawn through pilot hole 16 to the brake105. The resin is then left to cure to a shim 6, as in the embodiment ofFIG. 7.

Use of brake arrangement 119 rather than brake 19 reduces the amount ofsealing required around the brake region to a very small amount aroundtube 110, connection 115 and pilot hole 16. That in turn enables therequired level of vacuum to be achieved more easily.

The brake arrangement 119 of the third embodiment can of course be usedin the apparatus described with reference to the second embodiment. FIG.13 shows schematically a cross-section of a spar 3 and a cover whichforms part of the wing skin 5 b according to a fourth embodiment of theinvention. The embodiment illustrated in FIG. 13 is closely based on thesecond embodiment illustrated by FIG. 8 and the same reference numeralsare used to designate the parts that are substantially identical in bothembodiments. The brake arrangement shown in FIG. 8 is however replacedby a brake arrangement 119 similar to that illustrated in the thirdembodiment. Thus, the brake arrangement 119 comprises a brake 105 thatis separated from the pilot hole 16 in the wing skin 5 b by tubingcomprising tubes 110 a and 110 b. The brake 105 is connected via furthertubing 120 to a vacuum pump (not shown). The shim is formed in the shimcavity 40 in the same way as that described above with reference to FIG.8. In this case the shim so formed becomes bonded to the cover (wingskin 5 b). The surfaces of the spar flange 8 and wing skin 5 b aretreated accordingly prior to arrangement of the apparatus as shown inFIG. 13.

FIG. 14 shows an apparatus, according to a fifth embodiment of theinvention, for forming a shim between a section of wing skin 5 b and aspar 8. The spar 8 is connected to a rib post 250 including a rib postflange 252. This embodiment is similar to the fourth embodiment and thesame reference numerals are used to indicate the parts that areidentical. In this fifth embodiment however, the resin is drawn througha pilot hole 216 formed in the spar flange 8 and rib post flange 252 asopposed to drawing the resin through the wing skin 5 b (or cover). Thetube 110 a between the pilot hole 216 and the brake 105 is secured withbag tape 254. In this case the shim so formed becomes bonded to the sparflange 8. The surfaces of the spar flange 8 and wing skin 5 b aretreated accordingly before assembly of the components as shown in FIG.14.

As can be seen from FIGS. 13 and 14 the surface to which the shim, onceformed, becomes bonded depends on the component through which the resinis drawn. Thus, if the resin is drawn through the wing skin then theshim becomes bonded to the wing skin, whereas if the resin is drawnthrough the spar flange then the shim becomes bonded to the spar flange.Which of the arrangements in FIGS. 13 and 14 are used will depend onassembly issues. As mentioned above, the surface to which the shim is tobe bonded is roughened by grit blasting prior to formation of the shim,whereas the other surface is smoothed by treatment with release agent.For example, in FIG. 14 the spar flange is grit blasted and the wingskin (cover) is treated with release agent to enable the cured shim 6 toadhere to the spar and be released from the wing skin (cover).

It will be appreciated that various modifications may be made to theabove described embodiments without departing from the spirit of theinvention. For example, other resins can be used to create the shim. Forexample, a resin such as LY564/HY2954 (from Vantico Limited) could beused.

If a large gap is to be filled by the shim it may be beneficial toprovide a fibre material mat or other solid shim in the gap beforefilling with resin.

Whilst one bag is used to apply the vacuum to the system of the firstembodiment, several separate bags could be supplied. For example, onebag might be used to effect the fixing of the spar to the tool andfurther bags could be used to effect the flow of the resin into the gapbetween the spar flange and tool.

As opposed to using a coiled spring 20 as the resin inlet, a standardpipe with perforations or holes formed along its length could be used.

Further means can be implemented to improve flow of the resin into thegap between the spar flange and tool. For example, flow channels may beprovided to guide the flow of resin from the inlet pipe into the gap.Such channels may be provided by an element running parallel to andalong the length of the inlet pipe and could for example be in the formof a flat toothed belt (as described with reference to the secondembodiment), the gaps between the teeth of the belt forming the resinflow channels. Also the resin could be supplied under pressure.

A tool may of course be made to suit any size or shape of spar or otheraircraft component. Tools of different shapes may be made to form shimsfor aircraft components other than wing spars. The tool could of coursebe made of any suitable material able to be machined to provide asurface of a pre-determined shape to within a relatively small tolerance(such as less than 0.2 mm).

1-25. (canceled)
 26. A method of enabling two aircraft components to bejoined together, said method including the steps of providing a firstaircraft component having a surface to be joined to a correspondingsurface of a second aircraft component, said first and second componentsbeing so shaped that if joined there would be a gap defined between saidsurfaces of said first and second components, providing a resin infusionsystem comprising a source of resin, effecting flow of said resin fromsaid source of resin into said gap by means of suction, therebysubstantially filling said gap with resin, and curing said resin,wherein the flow of the resin out of the gap is restricted by means of abarrier and at least a part of the barrier is formed by a surface ofsaid resin infusion system.
 27. A method according to claim 26 whereinsaid surface of said resin infusion system is provided by a mouldingtool.
 28. A method according to claim 26, wherein said barrier is,during the filling of said gap with resin, removably fixed in positionrelative to said first aircraft component.
 29. A method according toclaim 28, wherein said barrier is fixed to said first aircraft componentby means of a pressure difference.
 30. A method according to claim 29,wherein a single vacuum pump is used both to cause said pressuredifference and to provide the suction that draws said resin into saidgap.
 31. A method according to claim 26, wherein said resin is curedwhile between said first aircraft component and said barrier.
 32. Amethod according to claim 31, wherein after said resin is cured saidfirst component and said barrier are separated.
 33. A method accordingto claim 26, wherein a surface of said first aircraft component isprepared so that adherence of said resin to said surface of said firstaircraft component is improved, a surface of said barrier is prepared sothat the adherence of the resin to said surface of said barrier isreduced to facilitate separation of said barrier from said resin oncecured.
 34. A method according to claim 26, wherein the method includes astep of joining said second aircraft component to said first aircraftcomponent, after said resin has cured.
 35. A method according to claim26, wherein a filter is provided to hinder flow of said resin out ofsaid gap.
 36. A method according to claim 26, wherein said firstaircraft component includes at least one aperture arranged so that thesuction is provided via said at least one aperture.
 37. A methodaccording to claim 34, wherein said resin enters said aperture, and themethod includes a step of remachining said aperture after said resin hascured.
 38. A method according claim 26, wherein the curing of said resinis effected by cold curing.
 39. A method according to claim 26, whereinsaid first aircraft component is formed of a composite material.
 40. Amethod according to claim 26, wherein said cured resin forms a shim. 41.A shim forming apparatus including a moulding tool having a surfaceshaped to receive a first aircraft component such that a gap is presentbetween the surface of said moulding tool and said first aircraftcomponent, said surface of said moulding tool being shaped to correspondto a surface of a second aircraft component, the apparatus furtherincluding a resin infusion system including a suction pump and a sourceof resin, the apparatus being so arranged that in use said gap betweenthe surface of the moulding tool and said first aircraft component isfilled with resin to form a shim.
 42. A shim forming apparatus accordingto claim 41, wherein said moulding tool has a portion that in use isable to sealingly engage with a portion of said first aircraftcomponent, to define a sealed region, which is connectable to a suctionpump so that in use suction is applied to said sealed region, therebyholding said first aircraft component in a fixed position relative tosaid moulding tool.
 43. A shim forming apparatus according to claim 41,wherein the apparatus further includes a vacuum bag that is attachableto said moulding tool and which, in use, enables suction to be appliedto said moulding tool to draw resin from said resin source into saidgap.
 44. A moulding tool suitable for use in a shim forming apparatus,said moulding tool having a surface shaped to receive a first aircraftcomponent such that a gap is present between said surface of saidmoulding tool and said first aircraft component, said surface of saidmoulding tool being shaped to correspond to a surface of a secondaircraft component, said moulding tool being so configured that it maybe arranged so that, in use, a gap formed between said surface of saidmoulding tool and such a first aircraft component is filled with resinto form a shim.
 45. A method of joining two aircraft componentstogether, said method including the steps of providing a first aircraftcomponent formed of a composite material having a surface to be joinedto a corresponding surface of a second aircraft component formed of acomposite material, said first and second components being so shapedthat if joined there would be a gap defined between said surfaces ofsaid first and second components, providing a resin infusion systemcomprising a source of resin, placing said first aircraft componentagainst a surface of said resin infusion system, effecting flow of saidresin from said source of resin into said gap by means of suction,thereby substantially filling said gap with resin, the flow of the resinout of the gap being restricted by means of a barrier, at least a partof said barrier being formed by a surface of said resin infusion system,and said barrier and said first aircraft component being, during thefilling of said gap, removably fixed in position relative to each otherby means of a pressure difference, curing said resin while between saidfirst aircraft component and said barrier so as to form a shim on saidfirst aircraft component, separating said first aircraft component andsaid barrier after said resin has cured, and joining said secondaircraft component to said first aircraft component and said shim. 46.An aircraft structure including a first aircraft component connected toa second aircraft component, wherein a shim is interposed between thefirst and second components, the shim having been formed by performanceof the method of claim
 40. 47. An aircraft structure including a firstaircraft component connected to a second aircraft component, wherein ashim is interposed between the first and second components, the shimhaving been formed by the use of the apparatus of claim
 41. 48. Anaircraft structure including a first aircraft component connected to asecond aircraft component, wherein a shim is interposed between thefirst and second components, the shim having been formed by the use ofthe moulding tool of claim 44.